In EEPROM memories, the logical value of a bit is stored in a memory cell, comprising a state transistor and a selection transistor.
The state transistor is generally a floating-gate transistor, comprising a control gate and a floating gate, and the information is expressed as a function of the charge on the floating gate. Typically, a negative charge on the floating gate corresponds to a state referred to as “erased” (the logical value of the bit stored is, for example, “0”), whereas as positive charge on the floating gate corresponds to a state referred to as “programmed” (the logical value of the stored bit is, for example, “1”).
Generally speaking, the selection transistor allows the access to the state transistor to be controlled. Its source is connected to the drain of the state transistor, and the source of the state transistor is connected to a source line.